Add a cpuns command

This command lets you ssh to a system with the cpu command.
You can then run this command, with or without arguments,
and it will give you a cpu environment.

A typical way to run it:
sudo -E unshare -m cpuns

The -E is important to get the SUDO_UID and SUDO_GID

Signed-off-by: Ronald G Minnich <rminnich@gmail.com>

client/fns.go

@@ -7,6 +7,7 @@ package client
 import (
 	"bytes"
 	"crypto/rand"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -111,16 +112,17 @@ func (c *Cmd) HostKeyConfig(hostKeyFile string) error {
 // SetEnv sets zero or more environment variables for a Session.
 // If envs is nil or a zero length slice, no variables are set.
 func (c *Cmd) SetEnv(envs ...string) error {
+	var err error
 	for _, v := range envs {
 		env := strings.SplitN(v, "=", 2)
 		if len(env) == 1 {
 			env = append(env, "")
 		}
 		if err := c.session.Setenv(env[0], env[1]); err != nil {
-			return fmt.Errorf("Warning: c.session.Setenv(%q, %q): %v", v, os.Getenv(v), err)
+			err = errors.Join(fmt.Errorf("Warning: c.session.Setenv(%q, %q): %v", v, os.Getenv(v), err))
 		}
 	}
-	return nil
+	return err
 }
 
 // SSHStdin implements an ssh-like reader, honoring ~ commands.
@@ -202,8 +204,7 @@ func GetHostName(host string) string {
 
 // GetPort gets a port. It verifies that the port fits in 16-bit space.
 // The rules here are messy, since config.Get will return "22" if
-// there is no entry in .ssh/config. 22 is not allowed. So in the case
-// of "22", convert to defaultPort.
+// there is no entry in .ssh/config.
 func GetPort(host, port string) (string, error) {
 	p := port
 	verbose("getPort(%q, %q)", host, port)

cmds/cpu/cpu.go

@@ -115,9 +115,6 @@ func getHostName(host string) string {
 }
 
 // getPort gets a port.
-// The rules here are messy, since config.Get will return "22" if
-// there is no entry in .ssh/config. 22 is not allowed. So in the case
-// of "22", convert to defaultPort
 func getPort(host, port string) string {
 	p := port
 	verbose("getPort(%q, %q)", host, port)
@@ -127,7 +124,7 @@ func getPort(host, port string) string {
 			p = cp
 		}
 	}
-	if len(p) == 0 || p == "22" {
+	if len(p) == 0  {
 		p = defaultPort
 		verbose("getPort: return default %q", p)
 	}

cmds/cpu/doc.go

@@ -254,4 +254,11 @@
 // If you want to learn more read the factotum paper by Grosse et. al. and the original
 // Plan 9 papers on cpu, but be aware there are many subtle details visible only
 // in code.
+//
+// You can now tentatively talk to standard sshd.
+// Here is an example:
+// ./cpu -nfs=true -9p=false -d -key ~/.ssh/homemac -sp 22 127.0.0.1
+// A few things: 9p has to be off, since sshd don't understand the -9 switch
+// Failing to Setenv is no longer an error, so you may not be able to set things
+// like SHELL.
 package main

cmds/cpuns/main_linux.go

@@ -6,13 +6,15 @@ package main
 
 import (
 	"flag"
+	"fmt"
 	"log"
 	"os"
-	"runtime"
+	"strconv"
+	"strings"
 	"syscall"
 
+	"github.com/moby/sys/mountinfo"
 	"github.com/u-root/cpu/session"
-	"golang.org/x/sys/unix"
 )
 
 var (
@@ -21,30 +23,38 @@ var (
 	v = func(string, ...interface{}) {}
 )
 
-// os.Unshare is tricky to call. Go runtime does not really handle it
-// correctly; if you have muiltiple procs, it only runs for one of them.
-// init functions run in single-process context, or so we understand ...
-func init() {
-	m := runtime.GOMAXPROCS(1)
-	if err := syscall.Unshare(syscall.CLONE_NEWNS); err != nil {
-		log.Fatalf("can not run if unshare fails: %v", err)
-	}
-	if err := unix.Mount("", "/", "", syscall.MS_REC|syscall.MS_PRIVATE, ""); err != nil {
-		log.Fatalf(`unix.Mount("", "/", "", syscall.MS_REC|syscall.MS_PRIVATE, ""); %v`, err)
-	}
-	runtime.GOMAXPROCS(m)
-}
-
 func verbose(f string, a ...interface{}) {
 	v("CPUNS:"+f, a...)
 }
 
+func checkprivate() error {
+	mnts, err := mountinfo.GetMounts(mountinfo.SingleEntryFilter("/"))
+	if err != nil {
+		return err
+	}
+	if len(mnts) != 1 {
+		return fmt.Errorf("got more than 1 mount for /(%v):%v", mnts, os.ErrInvalid)
+	}
+	entry := mnts[0]
+	fmt.Printf("Optional is %q\n", entry.Optional)
+	isShared := strings.Contains(entry.Optional, "shared:1")
+	if isShared {
+		return fmt.Errorf("/ is not private")
+	}
+	return nil
+}
+
 func main() {
+	fmt.Printf("uid %v git %v", os.Getuid(), os.Getgid())
+	if err := checkprivate(); err != nil {
+		log.Fatal(err)
+	}
 	flag.CommandLine = flag.NewFlagSet("cpuns", flag.ExitOnError)
 	debug := flag.Bool("d", false, "enable debug prints")
 	flag.Parse()
 	if *debug {
 		v = log.Printf
+		session.SetVerbose(v)
 	}
 	args := flag.Args()
 	shell := "/bin/sh"
@@ -60,7 +70,38 @@ func main() {
 	// good way to pass it (it is passed as as switch in cpud).
 	// That is ok, 9p has never been that good on Linux.
 	s := session.New("", args[0], args[1:]...)
-	if err := s.Run(); err != nil {
+	if err := s.NameSpace(); err != nil {
 		log.Fatalf("CPUD(remote): %v", err)
 	}
+
+	if err := s.Terminal(); err != nil {
+		log.Printf("s.Terminal failed(%v); continuing anyway", err)
+	}
+
+	u, ok := os.LookupEnv("SUDO_UID")
+	if !ok {
+		log.Printf("no SUDO_UID; continuing anyway")
+	}
+	g, ok := os.LookupEnv("SUDO_GID")
+	if !ok {
+		log.Printf("no SUDO_GID; continuing anyway")
+	}
+
+	uid, err := strconv.Atoi(u)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	gid, err := strconv.Atoi(g)
+	if err != nil {
+		log.Fatal(err)
+	}
+	c := s.Command()
+	c.Stdin, c.Stdout, c.Stderr = s.Stdin, s.Stdout, s.Stderr
+	c.SysProcAttr = &syscall.SysProcAttr{}
+	c.SysProcAttr.Credential = &syscall.Credential{Uid: uint32(uid), Gid: uint32(gid)}
+	if err := c.Run(); err != nil {
+		log.Fatalf("Run %v returns %v", c, err)
+	}
+
 }

go.mod

@@ -17,6 +17,7 @@ require (
 	github.com/go-git/go-billy/v5 v5.5.1-0.20240514075308-8f1b719cb6a2
 	github.com/google/uuid v1.5.0
 	github.com/mdlayher/vsock v1.2.1
+	github.com/moby/sys/mountinfo v0.7.1
 	github.com/shirou/gopsutil v3.21.11+incompatible
 	github.com/willscott/go-nfs v0.0.2
 	golang.org/x/exp v0.0.0-20230810033253-352e893a4cad
@@ -35,7 +36,6 @@ require (
 	github.com/miekg/dns v1.1.55 // indirect
 	github.com/pierrec/lz4/v4 v4.1.18 // indirect
 	github.com/rasky/go-xdr v0.0.0-20170124162913-1a41d1a06c93 // indirect
-	github.com/stretchr/testify v1.9.0 // indirect
 	github.com/tklauser/go-sysconf v0.3.11 // indirect
 	github.com/tklauser/numcpus v0.6.1 // indirect
 	github.com/u-root/uio v0.0.0-20230305220412-3e8cd9d6bf63 // indirect

go.sum

@@ -4,25 +4,19 @@ github.com/brutella/dnssd v1.2.9 h1:eUqO0qXZAMaFN4W4Ms1AAO/OtAbNoh9U87GAlN+1FCs=
 github.com/brutella/dnssd v1.2.9/go.mod h1:yZ+GHHbGhtp5yJeKTnppdFGiy6OhiPoxs0WHW1KUcFA=
 github.com/creack/pty v1.1.18 h1:n56/Zwd5o6whRC5PMGretI4IdRLlmBXYNjScPaBgsbY=
 github.com/creack/pty v1.1.18/go.mod h1:MOBLtS5ELjhRRrroQr9kyvTxUAFNvYEK993ew/Vr4O4=
-github.com/cyphar/filepath-securejoin v0.2.4 h1:Ugdm7cg7i6ZK6x3xDF1oEu1nfkyfH53EtKeQYTC3kyg=
-github.com/cyphar/filepath-securejoin v0.2.4/go.mod h1:aPGpWjXOXUn2NCNjFvBE6aRxGGx79pTxQpKOJNYHHl4=
 github.com/cyphar/filepath-securejoin v0.2.5 h1:6iR5tXJ/e6tJZzzdMc1km3Sa7RRIVBKAK32O2s7AYfo=
 github.com/cyphar/filepath-securejoin v0.2.5/go.mod h1:aPGpWjXOXUn2NCNjFvBE6aRxGGx79pTxQpKOJNYHHl4=
-github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
-github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
 github.com/gliderlabs/ssh v0.3.5 h1:OcaySEmAQJgyYcArR+gGGTHCyE7nvhEMTlYY+Dp8CpY=
 github.com/gliderlabs/ssh v0.3.5/go.mod h1:8XB4KraRrX39qHhT6yxPsHedjA08I/uBVwj4xC+/+z4=
-github.com/go-git/go-billy/v5 v5.5.0 h1:yEY4yhzCDuMGSv83oGxiBotRzhwhNr8VZyphhiu+mTU=
-github.com/go-git/go-billy/v5 v5.5.0/go.mod h1:hmexnoNsr2SJU1Ju67OaNz5ASJY3+sHgFRpCtpDCKow=
 github.com/go-git/go-billy/v5 v5.5.1-0.20240514075308-8f1b719cb6a2 h1:vWpyklHBOaIWDj1n3s/6M7rfLFDBXXbT1jrNOtBVo7Y=
 github.com/go-git/go-billy/v5 v5.5.1-0.20240514075308-8f1b719cb6a2/go.mod h1:7u9KSvLbAYN7/p0U+SsuzbbMuqCAk7MYkPI8l2+71s4=
 github.com/go-ole/go-ole v1.2.6 h1:/Fpf6oFPoeFik9ty7siob0G6Ke8QvQEuVcuChpwXzpY=
 github.com/go-ole/go-ole v1.2.6/go.mod h1:pprOEPIfldk/42T2oK7lQ4v4JSDwmV0As9GaiUsvbm0=
 github.com/golang/protobuf v1.5.3 h1:KhyjKVUg7Usr/dYsdSqoFveMYd5ko72D+zANwlG1mmg=
-github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/goexpect v0.0.0-20191001010744-5b6988669ffa h1:PMkmJA8ju9DjqAJjIzrBdrmhuuPsoNnNLYgKQBopWL0=
 github.com/google/goterm v0.0.0-20200907032337-555d40f16ae2 h1:CVuJwN34x4xM2aT4sIKhmeib40NeBPhRihNjQmpJsA4=
 github.com/google/uuid v1.5.0 h1:1p67kYwdtXjb0gL0BPiP1Av9wiZPo5A8z2cWkTZ+eyU=
@@ -49,25 +43,19 @@ github.com/mdlayher/vsock v1.2.1 h1:pC1mTJTvjo1r9n9fbm7S1j04rCgCzhCOS5DY0zqHlnQ=
 github.com/mdlayher/vsock v1.2.1/go.mod h1:NRfCibel++DgeMD8z/hP+PPTjlNJsdPOmxcnENvE+SE=
 github.com/miekg/dns v1.1.55 h1:GoQ4hpsj0nFLYe+bWiCToyrBEJXkQfOOIvFGFy0lEgo=
 github.com/miekg/dns v1.1.55/go.mod h1:uInx36IzPl7FYnDcMeVWxj9byh7DutNykX4G9Sj60FY=
-github.com/onsi/gomega v1.27.10 h1:naR28SdDFlqrG6kScpT8VWpu1xWY5nJRCF3XaYyBjhI=
+github.com/moby/sys/mountinfo v0.7.1 h1:/tTvQaSJRr2FshkhXiIpux6fQ2Zvc4j7tAhMTStAG2g=
+github.com/moby/sys/mountinfo v0.7.1/go.mod h1:IJb6JQeOklcdMU9F5xQ8ZALD+CUr5VlGpwtX+VE0rpI=
 github.com/onsi/gomega v1.33.1 h1:dsYjIxxSR755MDmKVsaFQTE22ChNBcuuTWgkUDSubOk=
 github.com/pierrec/lz4/v4 v4.1.14/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
 github.com/pierrec/lz4/v4 v4.1.18 h1:xaKrnTkyoqfh1YItXl56+6KJNVYWlEEPuAQW9xsplYQ=
 github.com/pierrec/lz4/v4 v4.1.18/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
-github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rasky/go-xdr v0.0.0-20170124162913-1a41d1a06c93 h1:UVArwN/wkKjMVhh2EQGC0tEc1+FqiLlvYXY5mQ2f8Wg=
 github.com/rasky/go-xdr v0.0.0-20170124162913-1a41d1a06c93/go.mod h1:Nfe4efndBz4TibWycNE+lqyJZiMX4ycx+QKV8Ta0f/o=
 github.com/rogpeppe/go-internal v1.11.0 h1:cWPaGQEPrBb5/AsnsZesgZZ9yb1OQ+GOISoDNXVBh4M=
 github.com/shirou/gopsutil v3.21.11+incompatible h1:+1+c1VGhc88SSonWP6foOcLhvnKlUeu/erjjvaPEYiI=
 github.com/shirou/gopsutil v3.21.11+incompatible/go.mod h1:5b4v6he4MtMOwMlS0TUMTu2PcXUg8+E1lC7eC3UO/RA=
-github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
-github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
-github.com/stretchr/testify v1.8.0 h1:pSgiaMZlXftHpm5L7V1+rVB+AZJydKsMxsQBIJw4PKk=
-github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
 github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
-github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 github.com/tklauser/go-sysconf v0.3.11 h1:89WgdJhk5SNwJfu+GKyYveZ4IaJ7xAkecBo+KdJV0CM=
 github.com/tklauser/go-sysconf v0.3.11/go.mod h1:GqXfhXY3kiPa0nAXPDIQIWzJbMCB7AmcWpGR8lSZfqI=
 github.com/tklauser/numcpus v0.6.0/go.mod h1:FEZLMke0lhOUG6w2JadTzp0a+Nl8PF/GFkQ5UVIcaL4=
@@ -92,8 +80,6 @@ github.com/willscott/go-nfs-client v0.0.0-20240104095149-b44639837b00/go.mod h1:
 github.com/yusufpapurcu/wmi v1.2.3 h1:E1ctvB7uKFMOJw3fdOW32DwGE9I7t++CRUEMKvFoFiw=
 github.com/yusufpapurcu/wmi v1.2.3/go.mod h1:SBZ9tNy3G9/m5Oi98Zks0QjeHVDvuK0qfxQmPyzfmi0=
 golang.org/x/crypto v0.0.0-20220826181053-bd7e27e6170d/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
-golang.org/x/crypto v0.21.0 h1:X31++rzVUdKhX5sWmSOFZxx8UW/ldWx55cbf08iNAMA=
-golang.org/x/crypto v0.21.0/go.mod h1:0BP7YvVV9gBbVKyeTG0Gyn+gZm94bibOW5BjDEYAOMs=
 golang.org/x/crypto v0.22.0 h1:g1v0xeRhjcugydODzvb3mEM9SQ0HGp9s/nh3COQ/C30=
 golang.org/x/crypto v0.22.0/go.mod h1:vr6Su+7cTlO45qkww3VDJlzDn0ctJvRgYbC2NvXHt+M=
 golang.org/x/exp v0.0.0-20230810033253-352e893a4cad h1:g0bG7Z4uG+OgH2QDODnjp6ggkk1bJDsINcuWmJN1iJU=
@@ -102,8 +88,6 @@ golang.org/x/mod v0.12.0 h1:rmsUpXtvNzj340zd98LZ4KntptpfRHwpFOHG188oHXc=
 golang.org/x/mod v0.12.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/net v0.0.0-20220826154423-83b083e8dc8b/go.mod h1:YDH+HFinaLZZlnHAfSS6ZXJJ9M9t4Dl22yv3iI2vPwk=
-golang.org/x/net v0.23.0 h1:7EYJ93RZ9vYSZAIb2x3lnuvqO5zneoD6IvWjuhfxjTs=
-golang.org/x/net v0.23.0/go.mod h1:JKghWKKOSdJwpW2GEx0Ja7fmaKnMsbu+MWVZTokSYmg=
 golang.org/x/net v0.24.0 h1:1PcaxkF854Fu3+lvBIx5SYn9wRlBzzcnHZSiaFFAb0w=
 golang.org/x/net v0.24.0/go.mod h1:2Q7sJY5mzlzWjKtYUEXSlBWCdyaioyXzRB2RtU8KVE8=
 golang.org/x/sync v0.3.0 h1:ftCYgMx6zT/asHUrPw8BLLscYtGznsLAnjq5RH9P66E=
@@ -114,20 +98,17 @@ golang.org/x/sys v0.0.0-20200728102440-3e129f6d46b1/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220622161953-175b2fd9d664/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220728004956-3c1f35247d10/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220825204002-c680a09ffe64/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.18.0 h1:DBdB3niSjOA/O0blCZBqDefyWNYveAYMNF1Wum0DYQ4=
-golang.org/x/sys v0.18.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.20.0 h1:Od9JTbYCk261bKm4M/mw7AklTlFYIa0bIp9BgSm1S8Y=
 golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/term v0.0.0-20220722155259-a9ba230a4035/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
-golang.org/x/term v0.18.0 h1:FcHjZXDMxI8mM3nwhX9HlKop4C0YQvCVCdwYl2wOtE8=
-golang.org/x/term v0.18.0/go.mod h1:ILwASektA3OnRv7amZ1xhE/KTR+u50pbXfZ03+6Nx58=
 golang.org/x/term v0.19.0 h1:+ThwsDv+tYfnJFhF4L8jITxu1tdTWRTZpdsWgEgjL6Q=
 golang.org/x/term v0.19.0/go.mod h1:2CuTdWZ7KHSQwUzKva0cbMg6q2DMI3Mmxp+gKJbskEk=
 golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
@@ -139,8 +120,5 @@ golang.org/x/tools v0.12.0/go.mod h1:Sc0INKfu04TlqNoRA1hgpFZbhYXHPr4V5DzpSBTPqQM
 google.golang.org/grpc v1.56.3 h1:8I4C0Yq1EjstUzUJzpcRVbuYA2mODtEmpWiQoN/b2nc=
 google.golang.org/grpc v1.56.3/go.mod h1:I9bI3vqKfayGqPUAwGdOSu7kt6oIJLixfffKrpXqQ9s=
 google.golang.org/protobuf v1.30.0 h1:kPPoIgf3TsEvrm0PFe15JQ+570QVxYzEvvHqChK+cng=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
-gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
-gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

session/fns.go

@@ -16,7 +16,7 @@ func verbose(f string, a ...interface{}) {
 	v("session:"+f, a...)
 }
 
-func runCmd(c *exec.Cmd) error {
+func RunCmd(c *exec.Cmd) error {
 	sigChan := make(chan os.Signal, 1)
 	defer close(sigChan)
 	signal.Notify(sigChan, unix.SIGTERM, unix.SIGINT)

session/session.go

@@ -69,7 +69,7 @@ func (s *Session) DropPrivs() error {
 	uid := unix.Getuid()
 	verbose("dropPrives: uid is %v", uid)
 	if uid == 0 {
-		verbose("dropPrivs: not dropping privs")
+		verbose("dropPrivs: uid is 0: not dropping privs")
 		return nil
 	}
 	gid := unix.Getgid()
@@ -206,10 +206,10 @@ func (s *Session) Run() error {
 	c.Stdin, c.Stdout, c.Stderr, c.Dir = s.Stdin, s.Stdout, s.Stderr, os.Getenv("PWD")
 	dirInfo, err := os.Stat(c.Dir)
 	if err != nil || !dirInfo.IsDir() {
-		log.Printf("CPUD: your $PWD %s is not in the remote namespace", c.Dir)
+		log.Printf("CPUD: your $PWD %q is not in the remote namespace", c.Dir)
 		return os.ErrNotExist
 	}
-	err = runCmd(c)
+	err = RunCmd(c)
 	verbose("Run %v returns %v", c, err)
 	if err != nil {
 		if s.fail && len(wtf) != 0 {
@@ -237,3 +237,60 @@ func New(port9p, cmd string, args ...string) *Session {
 	// so we had a way out!
 	return &Session{msize: 64 * 1024, Stdin: os.Stdin, Stdout: os.Stdout, Stderr: os.Stderr, port9p: port9p, cmd: cmd, args: args}
 }
+
+// The following two functions were set up for cpuns.
+// They provide a bit more flexibility in setting things
+// up until we can agree on how it should all work.
+// Side note: it's probably time to remove all the
+// wtf support, above; it has been years since we needed it.
+// Run starts up a remote cpu session. It is started by a cpu
+// daemon via a -remote switch.
+
+// NameSpace prepares the namespace for the session.
+func (s *Session) NameSpace() error {
+	var errs error
+
+	if err := runSetup(); err != nil {
+		return err
+	}
+	if err := s.TmpMounts(); err != nil {
+		verbose("TmpMounts error: %v", err)
+		s.fail = true
+		errs = errors.Join(errs, err)
+	}
+
+	verbose("call s.NameSpace")
+	err := s.Namespace()
+	if err != nil {
+		return errors.Join(errs, fmt.Errorf("CPUD:Namespace: %v", err))
+	}
+
+	// The CPU_FSTAB environment variable is, literally, an fstab.
+	// Why an environment variable and not a file? We do not
+	// want to require any 9p mounts at all. People should be able
+	// to do this:
+	// CPU_FSTAB=`cat fstab`
+	// and get the mounts they want. The first uses of this will
+	// be building namespaces with drive and virtiofs.
+
+	// In some cases if you set LD_LIBRARY_PATH it is ignored.
+	// This is disappointing to say the least. We just bind a few things into /
+	// bind *may* hide local resources but for now it's the least worst option.
+	if tab, ok := os.LookupEnv("CPU_FSTAB"); ok {
+		verbose("Mounting %q", tab)
+		if err := mount.Mount(tab); err != nil {
+			verbose("fstab mount failure: %v", err)
+			// Should we die if the mounts fail? For now, we think not;
+			// the user may be able to debug. Just record that it failed.
+			s.fail = true
+		}
+	}
+
+	return nil
+}
+
+// Command returns an exec.Command that users can additionally modify.
+// This will all certainly change.
+func (s *Session) Command() *exec.Cmd {
+	return exec.Command(s.cmd, s.args...)
+}